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slip_manual_setup(7)
Contents
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slip_manual_setup - Describes how to manually set up the
Serial Line Internet Protocol (SLIP)
The Serial Line Internet Protocol (SLIP) is a protocol
used to run IP over serial lines, including RS-232 cables
connecting two systems and telephone circuits. Unlike Ethernet,
a serial line provides a point-to-point connection
between only two hosts. Like Ethernet, TCP/IP commands
(such as rlogin, ftp, and ping) can be run over the SLIP
connection.
Note that although you do not use a network interface with
SLIP, you must have a network interface configured on your
system for the network daemons (such as nfsd and rwhod) to
run properly. The network interface must be configured
with a new IP address. For example, if you have a personal
computer that you use at home and in the office, do
not use the same IP address for the network interface at
home as you use in the office. Use the netsetup utility
for the initial SLIP configuration. If you need to change
the IP address, see the Changing the IP Address section in
this reference page.
You can use either the routed or the gated daemon to manage
routing, if you are not using the SLIP connection
solely to communicate between the two systems making the
connection.
If you plan to use a system as an IP router, it must be
configured to allow the forwarding of IP packets. For more
information on setting a system up as an IP router, see
the Network Administration: Connections manual and
iprsetup(8).
You should restart the routed or gated process if either
was running prior configuring the SLIP interface with the
ifconfig command. This ensures that the SLIP interface is
recognized by the routed or gated daemon.
USING SLIP PHYSICAL CONNECTIONS [Toc] [Back] You can use SLIP to connect systems either directly (using
a null modem) or over telephone lines using modems.
If you connect the systems directly, use an RS-232 cable
to connect the serial ports on the two hosts. The cable
used must be a null modem cable, such as BC22D-xx, (where
xx varies depending on the length of the cable).
You can use this method for hosts in close proximity to
each other. The maximum length of this type of connection
is defined by the RS-232 standard.
If the systems are not in close proximity to each other,
you can connect them using telephone line and modems. To
use this kind of connection, attach a modem to a serial
port on both hosts so that the two hosts can establish a
serial connection between them. You can use an RS-232
cable connected to the serial port on the host. This cable
must be a straight-through cable such as BC22E-xx or
BC22F-xx and the modems must be set to 8 bit no parity.
SLIP works best when hardware control flow is used. High
speed modems often fall-back to a lower data rate when
line degradation occurs. To support hardware flow control
you must use 25 pin connectors.
Note
Do not use XON/XOFF flow control. It will corrupt the
data stream causing the TCP layer over IP to issue
retransmit requests for over-runs.
The modems you use with SLIP should be able to handle a
baud rate of 38,400. If the modems you plan to use cannot
handle a baud rate of 38,400, you should set them to the
highest baud rate to which they can be set. For example,
DEC V32 modems can handle baud rates up to 19,200; however,
they cannot be locked at this baud rate. The highest
baud rate they can be set to is 9,600.
The modems should also be V32bis compliant with V42bis
compression. Alternatively, the modems can support the
Microcom Network Protocol (MNP), because both V42bis and
MNP implement a subset of the other protocol.
Use either the tip or kermit command to connect the modem.
Note
Be sure you do not have a getty process running on the
port to which the modem is connected.
To use the tip command, perform the following steps: Add a
line such as the following to your /etc/remote file:
REMSYS:dv=/dev/tty00:br#38400:pa=none
In this example: Is the name of the remote system
to which you want to connect. Specifies the tty.
Note, if you are running UUCP, tty00 is renamed to
ttyd0. Specifies a baud rate of 38,400. Specifies
no parity. Issue the tip command. For example,
prompt> tip REMSYS
If the tip command is successful, you get a connected
message. Suspend the process and return to
local mode.
If you used the tip command to initiate the connection,
issue the Ctrl/Z key sequence. (If you use
Kermit, issue the Ctrl/C followed by Ctrl/Z key
sequence. Enter the slattach command. For example:
prompt> slattach /dev/tty00 38400 Use the ping
command to wake up the interface on the remote system.
For example: prompt> ping REMSYS
It may take a few ping messages to wake up the
remote interface.
Alternatively, you can leave slattach running on the
remote system and rely on modem passwords and callback for
security.
For more information on the tip command, see the tip(1)
reference page and the Command and Shell User's Guide.
To configure your system to use SLIP, perform the following
steps: Add the SLIP option to the host's kernel.
By default, an entry for SLIP exists in the system
configuration file, /sys/conf/HOSTNAME (where HOSTNAME
is the name of your system).
Note
The SLIP option is not included by default on 24 MB
configurations systems. On these systems, you must
configure the SLIP option into the kernel.
The entry appears as follows:
options SL
This entry provides the host with one SLIP interface
(sl0). You can override this option by specifying
the nslip parameter in the /etc/sysconfigtab
file. For example, the following example specifies
two SLIP interfaces (sl0 and sl1):
net: nslip=2
For more information, see the section on configuring
the kernel in the System Administration manual.
Add entries to the /etc/hosts file for the network
adapters at both ends of the SLIP network.
For example:
129.34.0.1 sys2_sl sys2_sl.sl.abc.com
129.34.0.2 hst2_sl hst2_sl.sl.abc.com Configure
the SLIP interfaces by using the ifconfig command.
For example: # ifconfig sl0 129.34.0.1
129.34.0.2 netmask 255.255.0.0
On hst2 , you could issue the following command: #
ifconfig sl0 129.34.0.2 129.34.0.1 netmask
255.255.0.0
In these examples, the first argument is the name
of the SLIP pseudodevice, the second argument is
the local address of the SLIP interface, the third
argument is the address of the SLIP interface on
the remote host, and the remaining arguments specify
the network mask.
For more information, see the ifconfig(8) reference
page. Attach a serial line to a SLIP interface by
using the slattach command.
You use the slattach command to select the serial
line that will be attached to the SLIP interface.
The slattach command is also used to enable or disable
the SLIP options. For more information on
specifying options, see the slattach(8) reference
page.
When you use the slattach command, you do not specify
the SLIP interface to be used (sl0, sl1,...).
Instead, the first configured SLIP interface (one
for which you issued an ifconfig command) that is
not already attached is used. You also specify the
baud rate for the serial connection with the slattach
command. If you do not specify a rate, it uses
the default rate of 9600 baud. The following is an
example of using the slattach command: # slattach
tty00 9600
In this example, tty00 attaches to a SLIP interface
and sets the baud rate to 9600. The connection will
use the options that were previously set. (When you
boot the system, no SLIP options are enabled.)
The following is another example of the slattach
command: # slattach +c -i tty00
In this example, tty00 attaches to a SLIP interface
running at 9600 baud (the default speed). TCP
header compression is enabled and ICMP traffic suppression
is disabled. (Disabling an option has no
effect, if it was previously disabled.)
For more information on the slattach command, refer
to the slattach(8) reference page.
After completing these steps, the SLIP network is available
as long as the physical connection is ready and the
slattach command is running. The ps command can be used to
ensure the slattach command is running. If at any time
the slattach command exits (due to a system or network
error), the command can be executed again to reestablish
the SLIP network.
The physical connection is always ready if a direct connection
is being used. For phone connections, the connection
is readied by manually dialing the modem on the local
system to connect to the modem on the remote system. Once
the remote modem answers, the data/talk button (or equivalent)
should be pressed to allow the modem on the local
host to assume control of the connection. Depending on
the type of modem used, the connection might take a few
seconds while the modems negotiate speeds, protocols, and
other session parameters before it is ready for use. The
connection should stay up until one side hangs up due to
some error or a user intentionally disconnects by pressing
the data/talk button.
STOPPING AND RESTARTING SLIP [Toc] [Back] You stop the SLIP network by using the kill command to
stop the running slattach process that has attached a
serial line to SLIP. You can restart the SLIP network by
reissuing the slattach command, which readies the physical
connection. When disabling a SLIP network that runs over a
phone connection, press the data/talk button on the modem
to hang up the line.
CHANGING THE IP ADDRESS [Toc] [Back] To change the IP addresses used on a SLIP interface do the
following: Issue the following command to stop the slattach
connection: # kill slattach Issue the ifconfig command
to deactivate the interface. For example: # ifconfig
sl0 down Issue the ifconfig command to delete the current
local SLIP address. For example: # ifconfig sl0 delete
15.141.63.153 Issue the ifconfig command to configure the
SLIP interface. For example: # ifconfig sl0 15.142.63.153
15.143.65.163
In this example, 15.142.63.153 is the local SLIP IP
address and 17.143.65.163 is SLIP IP address on the
remote system to which you will connect. Issue the
slattach command to attach the serial line to the
network interface.
Commands: ifconfig(8), netstat(1)
Network Administration: Connections
slip_manual_setup(7)
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